Patent GB-958607-A (GB)
Title: Production of siliceous pigments
IPC: D21H17/68
Filed: 1961-12-04
Abstract: Finely divided siliceous pigments are produced by a method which comprises diluting an aqueous alkali metal silicate solution containing at least 30 grams alkali metal oxide per litre with water to provide a solution having less than 15 grams alkali metal oxide per litre, <PICT:0958607/C1/1> promptly thereafter partially neutralizing the diluted solution to form an aqueous siliceous solution having a tendency to form silicate precipitate and mixing water soluble salt with the partially neutralized siliceous solution before water insoluble siliceous material appears therein whereby to precipitate siliceous pigment. In an example, water at 45 DEG C. is forwarded through conduit 1 past Venturi 2 which causes sodium silicate solution also at 45 DEG  C. to be inspirated and promptly diluted with water. The resulting solution is discharged into mixing block 3. Simulataneously, water is forwarded in conduit 4 past Venturi 5 which inspirates hydrochloric acid and dilutes it and passes it into mixing block 3.  The jets are so arranged that they discharge the liquids tangentially and spaced 180 degrees from one another. The streams are thereby mixed and the partially neutralized solution is discharged through conduit 7 into tank 8.  Tank 8 con tains an aqueous solution of calcium chloride and sodium chloride to precipitate siliceous material which is removed as a slurry by conduit 13 to be washed, filtered and dried.  To prevent sodium silicate passing through unprecipitated, a baffle (not shown) is disposed in the tank.  The pigments produced have the following composition (parts by weight). .SiO2.79.5 .CaO.7.2 .Fe2O3.0.10 .*R2O3.0.47 .NaCl.0.76 .* Mainly Al2O3 and .Fe2O3  Specification 942,263 is referred to.ALSO:<PICT:0958607/C3/1> Fine-divided siliceous pigments are produced by a method which comprises diluting an aqueous alkali metal silicate solution containing at least 30 grams alkali metal oxide per litre with water to provide a solution having less than 15 grams alkali metal oxide per litre, promptly thereafter partially neutralizing the diluted solution to form an aqueous siliceous solution having a tendency to form silicate precipitate and mixing water soluble metal salt with the partially neutralized siliceous solution before water insoluble siliceous material appears therein whereby to precipitate siliceous pigment. In an example, water at 45 DEG  C. is forwarded through conduit 1 past Venturi 2, which causes sodium silicate solution also at 45 DEG  C. to be inspirated and promptly diluted with water.  The resulting solution is discharged into mixing block 3.  Simultaneously, water is forwarded in conduit 4 past Venturi 5, which inspirates hydrochloric acid and dilutes it and passes it into mixing block 3.  The jets are so arranged that they discharge the liquids tangentially and spaced 180 degrees from one another.  The streams are thereby mixed and the partially neutralized solution is discharged through conduit 7 into tank 8.  Tank 8 contains an aqueous solution of calcium chloride and sodium chloride to precipitate siliceous material which is removed as a slurry by conduit 13 to be washed, filtered and dried.  To prevent sodium silicate passing through unprecipitated, a baffle (not shown) is disposed in the tank. The pigments produced have the following composition (parts by weight): .SiO2.79.5 .CaO.7.2 .Fe2O3.0.10 .*R2O3.0.47 .NaCl.0.76 *Mainly Al2O3 and Fe2O3  Specification 942,263 is referred to.ALSO:Aqueous pulp slurry containing 2% pulp by weight is beaten to 400 millilitres freeness (Canadian standard) and is mixed with 10% of a silica pigment (based on pulp content) which has been made by diluting an alkali metal silicate solution from a concentration of more than 30 gms. metal oxide per litre to less than 15 gms./litre, partially neutralising this diluted solution and precipitating silica by mixing with water soluble salt (see Division C4).  Sufficient aluminium sulphate is added to adjust the slurry to pH5.  The pulp is then sheeted.  The product has improved opacity and brightness.  Specification 942,263 is referred to.